Xerographic copying apparatus with intercepting means for carrier particles

ABSTRACT

A xerographic copying apparatus wherein a cylindrical xerographic surface travels past a development unit wherein a bucket conveyor draws batches of charged toner particles and spherical carrier particles from a magazine and dumps the withdrawn particles onto the xerographic surface so that the toner particles adhere to and convert electrostatic latent images into powder images. The carrier particles descend along the xerographic surface and are intercepted and returned into the magazine by an elastic strip which extends radially of the xerographic surface and defines therewith a clearance whose width is a fraction of the diameters of carrier particles. Those carrier particles which strongly adhere to the xerographic surface deform and are thus free to bypass the elastic strip.

United States Patent [191 Hartwig et al.

[451 Mar. 25, 1975 1 XEROGRAPHIC COPYING APPARATUS WITH INTERCEPTING MEANS FOR CARRIER PARTICLES [75] Inventors: Karl Hartwig, Unterhaching;

Juergen Vossnacke, Pullach, both of Germany [73] Assignee: Agfa-Gevaert Aktiengesellschaft,

- Leverkusen, Germany [22] Filed: Dec. 15, 1972' [21] Appl. No.: 315,482

[30] Foreign Application Priority Data Dec. 17, 1971 Germany 2162842 [52] US. Cl. 1'18/637, 117/17.5

[51] Int. Cl. 603g 13/00, 117 17.5

[58] Field of Search 118/1'04, 202, 203, 261,

[56] References Cited UNITED STATES PATENTS 3,356,067 12/1967 Krasnow et al...'. 118/261 3,424,131 l/l969 Aser et a1. 118/637 3/1969 Pease et a1. 118/637 Primary Examiner-Mervin Stein Assistant Examiner-Leo Millstein Attorney, Agent, or FirmMichue1 S. Striker [57] ABSTRACT A xerographic copying apparatus wherein a cylindrical xerographic surface travels past a development unit wherein a bucket conveyor draws batches of charged toner particles and spherical carrier particles from a magazine and dumps the withdrawn particles onto the xerographic surface so that the toner particles adhere to and convert electrostatic latent images into powder images. The carrier particles descend along the xerographic surface and are intercepted and returned into the magazine by an elastic strip which extends radially of the xerographic surface and defines therewith a clearance whose width is a fraction of the diameters of carrier particles. Those carrier particles which strongly adhere to the xerographic surface deform and are thus free to bypass the elastic strip.

1 Claim, 2 Drawing Figures XEROGRAPHIC COPYING APPARATUS WITH INTERCEPTING MEANS FOR CARRIER PARTICLES CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION The invention relates to xerographic copying apparatus and more particularly to improvements in xerographic copying apparatus wherein a mixture of toner particles and carrier particles is cascaded over a moving xerographic surface to effect the conversion of electrostatic latent images into powder images which are ready to be transferred onto paper sheets or the like. Still more particularly, the invention relates to improvements in means for intercepting toner and/or carrier particles during or subsequent to conversion of latent images into powder images.

It is already known to provide a xerographic copying apparatus with a rigid'intercepting device which is installed at or downstream of the development station. As a'rule, such intercepting device comprises a rigid blade-like member which makes an acute angle with the adjacent portion of the xerographic surface and acts as a means for returning carrier particles into a magazine from which a bucket conveyor or an analogous transporting device withdraws batches of tonercarrier mixture for delivery to a location where the contents of the buckets are dumped onto the moving xerographic surface. A drawback of such intercepting devices is that the carrier particles (such as small spheres or beads) are likely to jam between the rigid blade-like member and the xerographic surface, especially if the carrier particles advance toward the bladelike member in the direction in which the xerographic surface travels at and beyond the development station. This can result in damage to the highly sensitive xerographic surface or in substantial losses in carrier material if the gap between the xerographic surface and the I blade-like member is wide enough to allow the carrier particles to pass therethrough without jamming.

SUMMARY OF THE INVENTION An object of the invention is to provide a xerographic copying apparatus with novel and improved means for intercepting all or nearly all particles of developer material, especially carrier particles, in such a way that the intercepting means and/or'the intercepted particles are not likely to damage the xerographic surface.

Another object of the invention is to provide intercepting means which can be readily and conveniently adjusted to normally collect all particles of surplus developer material, even if the dimensions of such particles vary within a wide range.

A further object of the invention is to provide a xerographic copying apparatus with a novel development unit which embodies the improved intercepting means.

An additional object of the invention is to provide intercepting means which can be installed in existing types of xerographic copying apparatus.

The invention is embodied in a xerographic copying apparatus wherein a preferably cylindrical xerographic surface transports electrostatic latent images. The copying apparatus comprises a development unit having a magazine for a supply of intermixed toner particles and preferably spherical carrier particles, conveyor means for removing toner and carrier particles from the supply in the magazine and for dumping the thus removed particles onto the xerographic surface whereby at least some toner particles adhere to the xerographic surface and convert the latent images into powder images and the carrier particles descend by gravity along and some thereof adhere to the xerographic surface, and novel intercepting means for returning at least some of the carrier particles into the magazine. The intercepting means comprises at least one intercepting element having a preferably thin stripshaped elastically deformable portion extending close to .but being spaced apart from the xerographic surface. The width of the clearance between the intercepting element and the xerographic surface is preferably only a fraction of the diameters of carrier particles so that the intercepting element can remove all or nearly all carrier particles which adhere to the xerographic surface. Those carrier particles which adhere to the surface with a predetermined force deform and are thus free to bypass the intercepting element.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved xerographic copying apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary vertical sectional view of a xerographic copying apparatus which embodies the improved intercepting means fortoner and/or carrier particles; and

FIG. 2 is an enlarged view of the detail within the phantom-line circle A in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. l illustrates a portion of a xerographic copying apparatus which comprises an endless xerographic surface 7 applied to the periphery of a rotary drum 8 and serving to transport electrostatic latent images past a development unit including a magazine 15 the lower portion of which contains a supply 16 of a mixture 1 of toner and carrier particles. The carrier particle s la resemble globules or beads. An endless conveyor having a chain or belt 2 for a series of receptacles in the form of pivotable buckets 3 serves to transport batches of carrier-toner mixture 1 from the supply 16 to a dumping station 17 where the filled buckets 3 are tilted sufficiently to discharge their contents onto the xerographic surface 7 which is assumed to travel in the direction indicated by arrow 8 The endless chain or belt 2 of the conveyor is trained over several sprocket wheels or pultoner adhere to the image areas of the xerographic surface 7 in order to convert the latent image into a powder image pattern which is thereupon transferred onto sheet material in a manner well known from the art and not shown in the drawing.

The carrier particles la which are dumped at the station 17 descend by gravity by moving with and/or relative to the xerographic surface 7 (arrow 8) and are returned into the lower portion of the magazine by a novel intercepting device which includes two discrete units each of which can direct carrier particles In into the supply 16 so that the carrier particles can accumulate fresh toner particles prior to entering an oncoming bucket 3 for renewed transport to the dumping station 17. The upper unit of the intercepting device comprises a chute 9 of sheet metal or the like which extends substantially radially of the drum 8 and slopes downwardly to the extent which is necessary to insure that the carrier particles 1a descending onto its upper side can roll back into the supply 16. The right-hand end portion or edge portion 9a of the chute 9 is curved upwardly and is spaced apart from the xerographic surface 7, i.e., the parts 7 and 9a define a gap which is substantially parallel to the axis of the drum 8 and is wide enough to allow practically or completely unobstructed passage of all such carrier particles 1a which adhere to the surface 7 at the time they reach the edge portion 9a. Those carrier particles 1a which adhere to the xerographic surface 7 and advance therewith beyond the edge portion 9a normally constitute a relatively small fraction of the overall number of carrier particles la which are dumped onto the surface 7 at the station 17.

The second unit ofthe intercepting device comprises a support 10 which may consist of sheet metal and may form an integral or removable part of the magazine 15. This support is adjacent to but spaced apart from the xerographic surface 7 below the chute 9 and carries a substantially plate-like holder 11 which is adjustably secured thereto by one or more screws 13 or analogous fasteners so that it can be moved in directions indicated by a doubleheaded arrow 11. For example, the holder 11 may be provided with elongated slots, one for each fastener 13 and each extending substantially radially of the drum 8 so that, when the fasteners 13 are loose, the holder 11 can be shifted radially toward or away from the drum 8. The holder 11 serves as a base for a relatively thin, flexible and preferably elastic strip 12 which may consist of elastomeric synthetic plastic material and the underside of which may be glued or otherwise permanently or detachably secured to the upper side of the holder 11. As shown, the strip 12 (which constitutes a particle-removing element in the form of a blade or the like) has a portion 12 a which extends beyond the edge face 100 of the support 10 and the edge face 110 of the holder 11 toward the xerographic surface 7 and is sufficiently flexible to allow for the passage of those carrier particles 1a which adhere to the surface 7 with a predetermined force such as is likely to result in damage to the surface 7 if the strongly adhering carrier particles were stripped off by the element 12. The length of the unsupported portion 12a of the element 12 (as considered in the radial direction of the drum 8) is shown at 1, and such length may be in the range of a few millimeters.

In normal operation of the development unit (which embodies the magazine 15, the conveyor 2, 3 and the two-unit intercepting device), the major percentage of carrier particles In which are dumped onto the surface 7 at the station 17 will descend onto the chute 9 and will be automatically returned into the lower part of the magazine 15. The remaining carrier particles la ad vance through the gap between the edge portion 9a and the xerographic surface 7 and reach the non-supported portion 12a of the element 12 to be returned into the magazine 15 by travelling along the upper sides of the parts 12, 11 and 10 in that order. The edge face of the portion should not contact the xerographic surface 7 because this could adversely affect the xerographic copying operation, for example, by removing toner from the powder image which is being transported toward the transfer station of the copying apparatus. On the other hand, the portion 12a of the element 12 should separate from the xerographic surface 7 at least those carrier particles 1a which do not adhere with a substantial force. Therefore, the distance or clearance r between the surface 7 and the portion 12a of the element 12 is selected in such a way that it is between onetenth and one-half the diameter of smallest carrier particles 1a which are employed in the copying apparatus. For example, if the diameters of carrier particles la range between 0.6 and 0.8 millimeter, the distance or clearance rmay be in the range of0.l to 0.3 millimeter, preferably between 0.2 and 0.25 millimeter. It has been found that the last-mentioned range is particularly satisfactory to insure the retrieval of all loosely adhering carrier particles la.

It can happen that the mixture 1 which forms the supply 16 in the lower part of the magazine 15 contains carrier particles la whose diameters deviate from the diameters of the majority of carrier particles. For example, some of the carrier particles 1a may be so small that they can readily escape through the clearance r even if the width of this clearance is selected with a view to invariably intercept all loosely adhering carrier particles having known diameters. Also, it can happen that the attendant or attendants fail to properly select the width of the clearance r so that at least some of the carrier particles 1a (including those which do not adhere to the xerographic surface 7 with a substantial force) will bypass the portion 12a and will not be returned into the magazine 15. This can be readily remedied byadjusting the holder 11 relative to the support 10 so as to reduce the width of the clearance r.

On the other hand, if some of the carrier particles la adhere to the surface 7 with a force which, if overcome by the intercepting device of the present invention, would result in some or extensive damage to the surface 7, the elasticity of the portion 12a of the element 12 guarantees that the portion 120 is capable of yielding to such strongly adhering carrier particles 1a whereby the carrier particles advance beyond the mag azine 15 and can be collected in a separate receptacle (not shown) downstream of the development unit or are separated from the surface 7 in another suitable way not forming part of the present invention. The direction in which the unsupported portion 12a of the element 12 can yield when engaged by one or more carrier particles 1a which adhere to the xerographic surface with a predetermined force is indicated by the arrow 12.

An important advantage of the improved intercepting device is that, if properly adjusted, the elastically deformable element 12 invariably segregates from the xerographic surface 7 all such carrier particles 10 which can be removed without causing damage to the surface 7 so that the operation of the development unit is economical without, however, economizing to such an extent that the retrieval of carrier particles 1a would be promoted at the risk of damaging the surface 7. The chute 9 (which constitutes an optional feature of the intercepting device) relieves the second unit including the element 12, i.e., the chute 9 normally intercepts the majority of carrier particles la so that the carrier particles which advance toward and are engaged by the portion 12a include only those which cannot be separated from the surface 7 by gravity and/or by centrifugal force. The holder 11 can be provided with or can be moved relative to a scale which enables the operator to properly select the width of the clearance r for separation of all or nearly all carrier particles with the excepv tion of those whose separation would result or would be likely to result in damage to the xerographic surface 7. The exact composition of the material of the element 12 forms no part of this invention; this element may consist of any material which exhibits sufficient elasticity to yield to carrier particles la adhering to the surface 7 with a force which, if overcome by the element 12, would be likely to bring about damage to the surface 7. The inclination of the element 12 relative to the drum 8 can be varied within a wide range; it was found that an elastic element which extends substantially radially of the drum 8 is capable of intercepting all or nearly all carrier particles 1a which move beyond the chute 9 (with the exception of those particles which adhere to the xerographic surface 7 with a force exceeding a predetermined force).

The details of other parts of the copying apparatus form no part of the invention. Such other parts include a charging, an exposure, a transfer and a cleaning or discharge unit. Reference may be had to the commonly owned copending application Ser. No. 181,374 filed Sept. l7, 1971, now U.S. Pat. No. 3,734,604, by $205- tak et a].

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claim:

1. In a xerographic copying apparatus wherein a moving endless cylindrical xerographic surface transports electrostatic latent images, a development unit including a magazine for a supply of intermixed toner and substantially spherical carrier particles, conveyor means for removing toner and carrier particles from the supply in said magazine and for dumping the thus removed particles onto said xerographic surface at a first level whereby at least some toner particles adhere to said xerographic surface to convert said latent images into powder images and the carrier particles descend by gravity along and some thereof adhere to said xerographic surface, and intercepting means for returning at least some of the dumped carrier particles into said magazine, said intercepting means comprising an intercepting element extending substantially radially of said xerographic surface and having an elastically deformable substantially strip-shaped portion extending close to but being spaced apart from said xerographic surface at a second level below said first level, said deformable portion-of said intercepting element having an elongated edge defining with said xerographic surface a clearance whose width is between one-tenth and one-half the diameter of a carrier particle and the elasticity of said portion of said intercepting element being sufficient to enable said portion to yield to carrier particles which adhere to said xerographic surface with a predetermined force, said xerographic surface being arranged to travel in a direction from said first level to said second level so that the descending carrier particles travel toward said portion of said intercepting element by moving in the same direction as said xerographic surface and said intercepting means further comprising means for adjustably supporting said intercepting element so that the latter is movable relative to said xero graphic surface. 

1. In a xerographic copying apparatus wherein a moving endless cylindrical xerographic surface transports electrostatic latent images, a development unit including a magazine for a supply of intermixed toner and substantially spherical carrier particles, conveyor means for removing toner and carrier particles from the supply in said magazine and for dumping the thus removed particles onto said xerographic surface at a first level whereby at least some toner particles adhere to said xerographic surface to convert said latent images into powder images and the carrier particles descend by gravity along and some thereof adhere to said xerographic surface, and intercepting means for returning at least some of the dumped carrier particles into said magazine, said intercepting means comprising an intercepting element extending substantially radially of said xerographic surface and having an elastically deformable substantially strip-shaped portion extending close to but being spaced apart from said xerographic surface at a second level below said first level, said deformable portion of said intercepting element having an elongated edge defining with said xerographic surface a clearance whose width is between one-tenth and one-half the diameter of a carrier particle and the elasticity of said portion of said intercepting element being sufficient to enable said portion to yield to carrier particles which adhere to said xerographic surface with a predetermined force, said xerographic surface being arranged to travel in a direction from said first level to said second level so that the descending carrier particles travel toward said portion of said intercepting element by moving in the same direction as said xerographic surface and said intercepting means further comprising means for adjustably supporting said intercepting element so that the latter is movable relative to said xerograPhic surface. 